1. Technical Field
The present invention relates to a light source, a lighting device, a monitoring device, and a projector.
2. Related Art
Currently, a light source which uses laser beam source and supplies fundamental laser beam after converting its wavelength is known. This light source uses second-harmonic generation (SHG) element as a wavelength conversion element for converting wavelength of fundamental laser beam, for example. By the function of the SHG element, laser beam having desired wavelength can be supplied from a general-purpose laser beam source. Moreover, a structure which supplies a sufficient amount of laser beam can be provided by using the SHG element. As an example of the light source including the SHG element, JP-A-5-235441 discloses a light source which contains the SHG element within a resonator structure for resonating laser beam. In the resonator structure, fundamental laser beam is resonated to convert its wavelength into a desired wavelength, and the laser beam having the desired wavelength is extracted and supplied with high wavelength conversion efficiency.
According to the light source having the structure disclosed in JP-A-5-235441, a mirror having wavelength selectivity is provided within the resonator structure to reflect fundamental laser beam. However, even when the mirror having wavelength selectivity is provided, it is difficult to reflect all of the fundamental laser beam. Thus, there is a possibility that a part of the fundamental laser beam passes through the mirror and leaks out of the light source. For example, when an image display apparatus includes this light source and uses infrared light as the fundamental laser beam, the infrared light having great light energy has adverse effect on peripheral equipment such as a screen on which images are displayed. In case of a system which returns the infrared light toward the light source contained in an LD light source package, the infrared light has adverse effect on a temperature controller of the SHG element. In this case, appropriate temperature control is difficult. When a light output monitor is equipped, monitoring cannot be achieved in a normal condition due to the effect of the returned infrared light.